Which would mean you don't have a current user. You need to authenticate the user in your app.
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Brian RoachMar 22 '11 at 13:45

But i want to display the picture and name of any user visiting my page. Do i just create an app for that?
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JohanMar 22 '11 at 13:52

In order to do that, yes - the user would have to authenticate with facebook on your site using facebook connect and authorize you to have access to that information. You can't just access their facebook cookie and account.
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Brian RoachMar 22 '11 at 13:55